You’ve probably heard a lot about anti-polish rings for pistons and how great they are for your diesel engine.
These rings were developed for a single purpose: to remove carbon buildup from pistons. This kind of carbon buildup can cause problems throughout your engine, including your VGT.
But APRs can help with that.
In this article, we’re taking a look at how APRs work, why exactly they were developed, and what carbon buildup can do to your pistons.
What Do Anti-Polish Rings Do?
Just why are anti-polish rings so great for your diesel engine?
In short, the APR liner is designed to knock carbon off the piston.
In your EGR engines, exhaust gas goes back in the intake side of the engine, and because we’re introducing this exhaust gas back into the engine, larger amounts of carbon can build up on the pistons.
This can actually increase the amount of carbon that builds up on the top of the piston. This carbon would then go down the side of the piston and the top piston ring would stop floating.
Why Is It a Problem If the Top Ring Stops Floating?
The job of the top piston ring is to move back and forth as the piston moves up and down.
But, it doesn’t actually travel in a straight line. Its path has a slight arc to it as the throw of the crankshaft comes up and down. Because of this, two sides of the piston will wear more.
If your piston ring seizes and doesn’t float, you’ll end up with bore polish.
As the carbon moves down on the piston and the top ring seizes, you’ll get not just bore polish, but blowby and oil consumption as well. Anti-polish rings help stop this.
How Manufacturers Designed APRs
Manufacturers made EGR engines to help make emissions cleaner, but they didn’t realize that this design would create a problem with carbon buildup. They had to develop something to fix the problem, leading to APRs.
They developed both APR liners and pistons. This means they’ve taken the liner, machined out the top, and put in an insert.
The insert is a reduced diameter, covering just the very top travel of the piston. As the piston moves through the APR, it should then knock off the carbon.
What the APR Does
Calling it “anti-polish” might be a bit misleading, as the ring doesn’t polish anything. The APR knocks off chunks of carbon before it can collect in large amounts.
The ring knocks it off as soon as the piston comes up.
Ideally, the carbon would go straight out the exhaust, but because it has to travel through the exhaust valves, turbo, DPF, and after treatment, it’s important to get the particles as small as possible. This prevents damage to the after treatment.
Just What is Blowby?
Blowby is one of the symptoms of bore polish, and it’s measured in how much compression (or how much gas) is coming out of the crankcase.
A lot of gasoline engines have gone to a closed crankcase design. This means all the gases stay inside the engine instead of being vented externally.
On a diesel engine, though, there’s a crankcase vent, which is sometimes referred to as a blowby tube.
If the amount of pressure inside the engine becomes too great, it can blow out seals. You might have heard some drivers complain that their dipsticks are blown out. This happens when the pressure inside the crankcase has exceeded its ability to vent it.
What Leads to Crankcase Pressure?
One of the largest causes of crankcase pressure is when your piston rings can no longer seal to the cylinder walls.
Your cylinder walls have a crosshatch on them, which puts the right friction on the liner, matching with the piston ring. This is actually what you’re doing when you’re breaking in your engine: you’re seating the rings in the liner. As the piston goes up, air is compressed on top of the piston.
It isn’t actually the pistons that seal. They just provide the movement for the rings, which seal air to the cylinder wall.
If the liner has bore polish, the crosshatch has been worn away and the rings can no longer seal against the wall. This allows some of the air to go down past the piston rings.
Failing liners can cause damage downstream, including:
- Plugged DPF filter
- VGT nozzle ring damage from carbon striking it
- Seized VGT vanes from excessive soot buildup
APR liners can be a durable solution. They can’t completely eliminate the carbon from your diesel engine. They can break the carbon into tiny pieces, helping your EGR system better manage the pollutants.
HHP Can Help!
If you’re still wondering about APRs and whether they’re right for your engine, we can help!
Our ASE Certified staff is here to answer your questions and even provide diagnostic assistance. We want to make sure you’re getting the parts that will fit your engine and solve your problems.
It’s our goal to take the risk out of buying diesel engine parts. From diagnosis through delivery, we’re Highway & Heavy Parts!
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